Match value and return multiple headers

I have a sheet with row 1 as my header: ID #s. (over 274 of them)
I need search the rest of the rows for M and then return the ID#s.

Currently, I am using this in column A for row 2 as an example:

=INDEX($I$1:$JV$1, MATCH("M",INDEX(I2:JV2,0),0))

But this only returns the first ID# value with M. In some, but not the majority, I have more than one ID# with M. Does anyone know how I can return more than one header with the matching value (such as in row3)?

Thanks!
Holly

Perhaps something like this? Using array formulas

That is close, but each row needs to keep it own ID#s. The IDs are specific to each mutation.

For example: Row 2: 67909
Row 3: 64556, 64557, 64561, 64562, etc....

wow! That is awsome.

So I can appply that to other letters and sheets by modifying: If cell1 = "M" Then

Thanks!